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CHEM compostella > Organic chemistry > Flashcards

Organic chemistry Flashcards

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1
Q

functional group of thiol and thioesters

A

-SH
-RC=O-SR’

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2
Q

reason between diff in reactivity between alcohols and thiols

A

difference electronegativty between S and O (but both are polar covalent)

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3
Q

classification of alcohols

A

1ary 2ary 3ary
dependent on number of alkly groups connected on the carbon of the function group OH

!! thiols do not form H bonds but alcohols do

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4
Q

Reactive properties of the OH group in alcohols and phenols

A
  1. form H bonds
  2. Act as weak bases (protonates to give rise to oxonium ion ROH2+)
  3. Act as weak acids (deprotonated to give rise to alkoxide ion RO-)

!! equilibrium mostly favoured in the basic property, not acidic

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5
Q

are phenols more or less acidic than alcohols

A

phenols are more acidic

REASON: the phenoxide ion is resonance stabilised

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6
Q

dehydration of alcohols

A
  • produces alkene
  • requires H3O+ ions at high temps
  • removes hydroxy group
    -forms a minor and major product (major is the highest degree carbocation)
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7
Q

how does oxidation of alochols occur biologically?

A

-mediated via NAD+ and NADP+
-a base removes the OH proton and the alkoxide ion transfers a hydride ion (H-) to the coenzyme

!! H- hydride ion = [2e- + H+]

NAD+ + 2e- + 2H+ –> NADH + H+

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8
Q

alkene to alcohol

A

REAGENTS: water with presence of acid as catalyst

(for unsymmetrical alkenes, OH is added to the carbon having less number of hydrogen atoms)

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9
Q

oxidation of promary alcohol into aldehyde - selective oxidizing agent

A

PDC (pyridinium chlorochromate) -> controlled but mild so it stops at an aldehyde state of partial oxidation.

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10
Q

1 reaction we need to know for thiols

A

REAGENT: Br2/I2/O2

2R-SH –> R-S-S-R + 2HI
(gas in the hydrogen halogen depending on the one used)

!! S-S is the bond characteristic of the disulfides

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11
Q

imortance of S-S covalent bonds in the body

A

-can protect cells for oxidative degradation
-eg, glutathionine is oxidised to glutathione disulfide to remove harful oxidants

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12
Q

difference bwtween two families of carbonyl groups

A
  1. aldehydes and ketons have R and H groups that CANNOT act as leaving groups in nuc substitution
  2. COOH/COCl/etc have groups that can dettach and undergo nuc substitution

!! hence they have difference reactivities and reactions

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13
Q

what is the hybridisation of a carbonyl bond

A

C=O so sp2

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14
Q

nucleophilic substitution of carbonyl compounds

A

NUC SUBSTITUTION: creating a tetrahedral intermediate with sp3 hybridisation

  1. reduction to either a primary or secondary alcohol (LiAlH4, where H- is nuc, in the presence of H+ for protonation)
  2. reduction to a hydroxynitrile (HCN, where CN- is nuc)

!! biologically: to form alcohols the H- ions are donated by the coenzymes

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15
Q

hemiacetal and acetal formation from carbonyls

A

alcohol ROH molecule uses lone pair of electrons to act as a nucleophile and attack the delta+ carbon of carbonyl

SPONTANEOUS REACTION (equilibrium position is forwards)

WITHOUT ACID: product is an acetal: C of carbonyl is bonded to a OH and an OR’ group

WITH ACID CATALYST: product is a hemiacetal: C of carbonyl bonded to 2OR’ groups

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16
Q

carbonyl reacting with an amine

A

PRODUCT: imines R2C=NR
-requires a slightly acidic environment
-can only occur with primary amines (bcos nitrogen is trivalent to be neutral)

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17
Q

what is tatutomerism?

A

KETO/ENOL: constitutinal isomers (tautomers)
-start from original ketone
-removal of a H atom from C of carbonyl bond
-creates a highly negative Carbanion
-this delocalises the electrons and forms C=C bond while the C=O of the carbonyl is broken to C-O
-H attaches to C-O to form C-OH

hence: enols have C=C-OH

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18
Q

what are the conditions for keto-enol tautomerism to be possible (2)

A
  1. hydrogen must be in the alpha position to become deprotonated (ie. adjacent to the C=O of the carbonyl)
  2. must come in contact with a strong base ( to induce deprotonation)
  3. carbonyl has to be in excess otherwise it would just get continuously become deprotonated
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19
Q

aldol condensation process

A

1st reaction of kerbs cycle
-a carbonyl is transformed to enol tautomer using a strong base
-enol acts as an electrophile and attacks an aldehyde molecules
-forms C-C covalent bond
-ALDOL: contains both an aldehyde and an alcohol OH functional group

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20
Q

are carbanions/carbocations nucleophiles or electrophiles

A

ANION: nucleophiles
CATION: electrophile

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21
Q

structure of carboxylic acids

A

-COOH
-Carbon of functional group is sp2 hybridisation
-strongly held by H bonding and so they mainly exist as cyclic dimers

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22
Q

why are carboxylic acids so reactive

A

the oxygen in the C=O and C-OH bonds pull electrons away from the carbon of the functional group

creates a strong delta positive charge which means that it is a strong electrophile

HENCE: THEY ARE MORE REACTIVE THAN KETONES/ALDEHYDES (bcos they have double the electron pull)

!! H of COOH can also be deprotonated so they can undergo acid base reactions

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23
Q

can carboxylic acids have a basic character?

A

YES - in very acidic conditions

H+ ions can be added on the oxygen of the C=O and becomes C=OH

this is possible because of the stbilisation provided by the resonance

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24
Q

acid base reactions of carboxylic acids (2)

A
  1. with bases to give salts (eg. with NaOH to form sodium carboxylate COO-Na+)
  2. with water to form the deprotonated ion
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25
reactions that convert carboxylic acids into their derivative (6)
1. acid halide: COCl addition of H2O 2. ester: COO addition of alcohol with heat and H+ acid catalysis 3. acid anhydrase: C=OOC=O addition of a carboxylic acid with heat and H+ catalysis 4. amide: CONH addition of an amine (can be either primary ot secondary) 5. thioester: COS addition of a thiole with heat and H+ acid catalysis 6. acyl phosphate
26
What is the type of reactions carboxylic acids undergo to form their derivatives
NUC SUBSTITUTION: OH of COOH acts as the leaving group and the Nuc species attacking the carbonyl C (electrophile) is substituted into the molecule isntead
27
what is the acyl group of a carboxylic acid
R-C=O portion of molecule (ie. everything other than the OH leaving group)
28
if in a reaction a water molecule is released when a bond is made, what does this say about the bond?
it is weaker and it is prone to hydrolysis
29
two possibilities for ester hydrolysis
1. acid hydrolysis to form parents alcohol and acid 2. Saponification: alkali hydrolysis to form parent alcohol and the carboxylATE ION (protonation can then form the acid)
30
Are amides basic and if yes/no why?
NOT BASIC: the lone pair on the nitrogen can be delocalised over the carbonyl group. Hence the lone pair cannot be used and cannot be donated for protonation !! this lack of lone pair use also makes them weak nucleophiles
31
Rank all carboxylic acid derivative in inrcreasing reactivity
amide ester thioester anhydrase acyl chloride
32
use of thioester in biology
THIOESTER is more energentic and less stable than a CARBOXYLIC ACID: activation energy of the synthesis of a thioester is lower that the carboxylic acid !! the body uses thioester CoA which is transformed into a thioester in order to have more probable reactions
33
reduction of carboxylic acids
forms primary alcohols treatment with LiAlH4 (reducing agent) in dry conditions
34
what molecules as monosaccharides and how are they named
-polyhydroxyaldehydes (aldoses) OR ketones (ketoses) -derived from the oxidation of the primary (aldehyde) or secondary (ketone) OH group of a glycerol molecule NAMING: 1. prefix is the type of molecule (aldo- or keto-) 2. suffix is the chain length EG. aldotriose is an aldose molecule of 3C length
35
are monosaccharides chiral?
NO FOR KETONE STRUCTURES YES FOR ALDEHYDE STRUCTURES (exist as a pair of enantiomers) --> in nature, only one of the enantiomers is present which is the D glyceraldehydes
36
what is the conventional way to draw fisher structure for carbohydrates
vertical chain is the longest alkyl chain and the carbonyl group is on the top
37
carbs that we need to know the fisher structure for
D-GLUCOSE: an aldose RLRR D-FRUCTOSE: a ketohexose LRR D-GALACTOSE: an aldose RLLR D-RIBOSE: aldopentose RRR 2DEOXY-D-RIBOSE: aldopentose with same structure as ribose but the O removed at C2 glucose and galactose are C4 epimers
38
what are epimers?
monosacharides where we have reversed the configuration of only one carbon cetner eg. galactose is a C4 epimer of glucose
39
what is the arrangement of monosacharides in water
closed CYCLIC rings REASON: the aldehyde of aldoses combine with the OH groups on the SAME molecule to form hemiacetal formation --> causes the cyclic closure of the molecule !!! this is a spontaneous process
40
what position does the closed cyclic version of glucose take
name: glucopyranose (a/b) formation of intramolecular bond between the COH and the OH at C5 !! cyclisation gives rise to two new isomers at C1 --> alpha glucose with OH DOWN and beta glucose with OH UP --> called teh HAYWORTH structures
41
which type of glucopyranose is more stable? + reason
beta is more stable spontaneous ratio in water of beta:alpha glucose is 2:1 REASON: OH groups in beta glucose is in the equatorial position (least steric hinderence between the OHs)
42
structual properties of the alpha and beta glucopyranoses
melting points are almost the same (around 145-150) optical power is very different: alpha rotates light by a much larger angle (112 vs 18 degress)
43
what is the cyclisation of fructose
forms alpha or beta fructofuranose which means it is a 5 point compounds
44
what are anomers
the beta and alpha conformations created by the spontaneous cyclisation of monosaccarides
45
what is mutarotation
the chain in optical rotation observed when pure alpha or beta anomer is dissolved in water present due to the free conversion between the alpha to the hemaicetal form and then to the beta form
46
what are reducing sugars + test for them
a sugar that can reduce another substance (hence is oxidised itself) !! fehlins or tollens to test for the aldehyde oxidation GLUCOSE -- oxidised to gluconic acid !!! quantifiable extent of reducing sugar can be achieved from photospectrometry
47
what is the difference of oxidation of glucose from lab reagents vs in the body?
1. in labs glucose is oxidised to gluconic acid (carboxylic acid group) 2. in body a specific enzyme interacts and oxidises glucose into glucoronic acid (contains BOTH a carboxylic acid and an aldehyde group)
48
glycoside formation of monossacharides
for cyclic monossacharides: reaction with an alchol forms hemiacetal and reaction with a second alcohol forms acetal !! bond formed is a glycosidic bond and forms at the anomer position of the monossacharide
49
dissacharides and their monomers
1. maltose: 2glucose alpha(1-4) 2. cellobiose: 2glucose beta(1-4) 3. sucrose: gluc + fruct (1-2) !! not reducing sugar bcos aldehyde group is removed 4. lactose: gluc + galactose b(1-4)
50
why are dissacharides still reducing sugars
postive test with fehlings indicates that they still have an aldehyde group this is bcos the glycosidic bond is between C1-4 and so the carbonyl bond is not affected
51
O and N linked glycosidic bonds
WHEN SUGAR IS BOUND TO RESIDUE (serine or asparagine) O-linked glycoproteins: covalent bond is between oxygen and the anomeric position - SERINE N-linked glycoproteins the covalent bond is between nitrogen and the anomeric position - ASPARAGINE !! the residue is called the aglycon
52
2 types of polyssacharides
1. Homopolysaccharides (one type of monosaccharide) 2. Heteropolysaccharides (different types of monosaccharides) !! both can be both linear or branched
53
types of pollyssacharides to know
1. amylose: 1-4 and unbranched 2. amylopectin: 1-4 and 1-6 and branched (every 20 units) 3. glycogen: made of amylose and amylopectin, so both 1-4 and 1-6 and branched (every 10 units, so twice as branched as amylopectin) 4. cellulose
54
function of glycogen
storage of glucose , isnt affected by osmotic potential, and high energy density bcos of branching
55
ways of characterising lipids
1. hydrolysable: can be converted into smaller molecules by hydrolysis (waxes/triglycerides/ phospholipids)
56
what compounds are hydrolysable lipids derived from
fatty acids long CH chain with a terminal COOH. longer than 5 carbon atoms form micelles in water (COOH positioned on the outside)
57
configuration around double bond in natural unsaturated fatty acids
cis form
58
MPs of unsaturated and saturated fatty acids comparison
saturated: van der waals, higher MP unsaturated: van der walls but MP is lower bcos of kinks from the double bond - doesnt allow close packing of molecules
59
IUPAC nomenclature of fatty acids
number of carbons starting from COOH eg. 18:1, Delta9 where 18 = number of carbons 1 = number of double bonds 9 = position of the double bond eg2. 20:5, Delta5,8,11,14,17
60
structure of waxes
esters formed from a fatty acids with a long alcohol - condensation reaction which eliminates a water molecule RCOOR' functional group (completely apolar and hydrophobic)
61
structure of triglycerides
3 esters made of a molecule of glycerol and 3 fatty acid chains (condensation reaction) - in the body this condensation can be sequential so it is more common that the 3 alkyl chains are different CH2(OH)CH(OH)CH2(OH) glycerol
62
are triglycerides chiral?
yes IF the 3 alkyl chains are different - it becomes chiral around the center carbon of the glycerol
63
function of triglycerides
chemical compounds used to store energy --> they give the greatest amount of enregy by degraded (than carbs and proteins)
64
fat vs oil
fat = saturated lipids, solid at room temperature oil = unsaturated lipids (C=C), liquid at room temperature
65
hydrolysis of triglycerides
ester hydrolysis --> use of water in wither acidic or alkaline (saponification) conditions OR: enzymes (LIPASES) naturally in the body - independent to the length of the fatty acid chain
66
what is the position of equilibrium for ester formation
K is close to 1 so neither side is truly favoured/not favoured
67
glycerophospholipid structure
molecule of glycerol with 2 fatty acid chains and phosphatidic acid !! all 3 bonds are ester bonds
68
isomer def
same molecular formula but diff structural formula and or disposition of functional groups
69
what properties do enantiomers have in relation to eachother
1. identical chemical physical properties (MP/BP/density) 2. diff optical activity (rotate PPL by the same angle in opposite directions)
70
what are meso compounds
molecules that look like they should be enantiomers bcos they have flipped chiral center, but are optically inactive bcos of a central line of symmetry
71
consequence on heat of combustion when increasing the alkane length
increases
72
heterolytic vs homolytic bond break
hetero: electrons are shared asymmetrically, both go to one atom -> use full arrow homo: electrons are shared symmetrically, one goes to each original atom --> use half arrow
72
electrophile and nucleophile def
electrophile: accept electron pairs (sometimes positive) nucleophiles: have lone electron pairs to donate (usually negative)
73
trend in strength of nucleophiles
increased basicity compounds with sulfur (HS-/RS-) are stronger than oxygen based compounds (OH-) negative are stronger than neutral
74
what causes the stability of aromatic compounds
orbitals of the carbon atoms are on the same plane, there is a cloud of delocalised electrons.
75
what is the OMP rule for aromatic compound nomenclature
O: ortho (1,2 positions) M: meta (1,3 positions) P: para (1,4 positions)
76
relationship between classification of amines and their basicity
tertiary are the most basic

CHEM compostella (3 decks)

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